Jupiter and its moons are occulted!
BY MARK ARMSTRONG
Posted: 13 July 2012
Jupiter and its moons move behind the bright limb of the Moon in the early hours of 15 July, to emerge minutes later from behind the dark limb. A superb photographic opportunity! AN graphic by Greg Smye-Rumsby.
A very rare event, especially from the UK, occurs in the pre-dawn skies of 15 July. A 25.7-day old moon will approach Jupiter in the wee small hours and finally moves in front of the gas giant at around 2.55am BST for observers in London. As with many exciting events from these shores, the observing circumstances are not ideal with a huge chunk of the country from north of the Midlands missing out completely and those favoured having to battle again the very low altitude (10 degrees) above the eastern horizon.
In addition to the total occultation there will be a chance to see a grazing occultation of Jupiter along a broad swathe some 120 kilometres wide. The northern limit of the graze line runs from the Welsh coast at Llantwit Major (3.04am BST), across to the Midlands south of Leicester and to the Lincolnshire coast at Sutton-at-sea (3.06am). For observers north of this line the Moon will just miss Jupiter's northern limb. Observers along the southern graze limit will see almost all of Jupiter occulted save for a minute section of the northern limb. The track runs from the Dorset coast near Kimmeridge (2.55am to 3.10am), across Bournemouth, Harrow and Barnet in N. London and finishes on the Norfolk coast just south of Great Yarmouth (2.57am to 3.12am). South of this line all of the gas giant will be occulted, including most of Greater London, the Isle of Wight, Sussex and Kent. From Greenwich, first contact is at 2.55am, with the total occultation lasting from 3.01am to 3.06am and last contact at 3.12am.
The graze line for the lunar occultation of Jupiter and its moons cuts right through England, north of the Home Counties. Below Jupiter's central graze line, observers will see a full occultation. North of this line, observers will see the Moon narrowly miss Jupiter. The same principle also works for the Galilean satellites. AN graphic by Greg Smye-Rumsby.
A really exciting bonus is that all the Jupiter's Galilean satellites are occulted too! Io and Europa, to Jupiter's west, are occulted before their parent, with Ganymede and Callisto having to wait until after Jupiter. It's worth making a special effort to find a good observing site for this event and making accurate timings of the disappearances and reappearanes of Jupiter and its moons. Astrophotographers also have a great opportunity to attempt some video in addition to the usual stills. So let's hope for a clearance in the appalling weather and set those alarms! If you are successful in securing some images then please share your success with us at gallery2012 @ astronomynow.com.